The purpose of this research is twofold: (1) to identify variables which discriminate between patients who refuse and those who agree to participate in clinical trials among patients eligible for clinical trials; and (2) to develop instruments which document recruitment and system characteristics that enable efficient identification and enrollment of patients in clinical trials. A model for viewing decision-making under uncertainty about health related matters provided direction for instrument development and data collection. Major elements of the model are: personal characteristics, perceived benefits, perceived barriers, perceived threats, symptoms, health motivation, and cues to action. A descriptive design will be employed. Four hundred subjects will be derived from patients eligible for participation in Cardiac Arrhythmia Suppression Trials (CAST). At the time a decision is made regarding participation in the CAST study, subject will be identified as enrolled (N=200) or refusing enrollment (N=200) and categorized accordingly. Patients in both groups will be asked at the time of declaring their decision to submit to an interview. After obtaining informed consent, data will be obtained via structured interview and/or self-report instruments (to be developed). Data will be collected at each site and mailed weekly to the P.I. who will maintain it in a locked file cabinet. Data will be coded and checked for accuracy and given to the consulting statistician for analysis and interpretation. Data analysis will include descriptive and inferential statistical techniques. Dissemination of findings will include presentations at professional meetings, publications and workshops.